Eleven Secret Service agents have been placed on leave for bringing up to 21 prostitutes to their hotel in Cartagena, Colombia, during a Presidential visit last week. Much criticism has focused on the possible threats to national security this posed — Sen. Susan Collins asked if the women could have been linked to terrorism. So far, there's no evidence of that — but it's not the only link the administration has to worry about. Many prostitutes in Colombia are victims of sex trafficking, often by former leaders of drug cartels.

Sex trafficking became common in Colombia after the collapse of the cartels in the late Nineties, according to Teresa Ulloa Ziaurriz, the Coaltion Against Trafficking in Women's regional director for Latin America, when former drug traffickers turned to human trafficking instead. Today, says Ulloa Ziaurriz, there's a lot of sex tourism in Cartagena and a few other Colombian cities, organized "by former members of the drug cartels that use their criminal structure to control the trafficking of women and girls."

Robin Kirk, program director of the Duke Human Rights Center and author of "More Terrible Than Death: Massacres, Drugs and America’s War in Colombia," told me that while she couldn't say for sure how much money paid to prostitutes in Colombia went into the pockets of current or former drug lords, prostitution and drug dealing have been intimately linked in Colombia. "Trafficking is trafficking," she explains, and people involved in one form were likely involved in others. She also notes that it would have been hard for Secret Service agents to determine whether the women they brought back to the hotel had ever been victims of trafficking — sex workers who have been trafficked may not say so, even if a client asks. And many clients don't — says Kirk, "Most people who use prostitutes don't have ethics on their mind."

MANDEL NGAN / Getty Images

The Hotel Caribe in Cartagena, where the Secret Service agents allegedly hired the sex workers.

The Secret Service apparently knows the identities of the sex workers who visited the hotel in Cartagena — they had to leave their IDs at the front desk before going to the Secret Service members' rooms. This might make it easier to determine whether they were ever trafficking victims or linked to organized crime.

If they are linked to the drug trade, it could be pretty embarrassing for Obama. He took a strong anti-drug stance on his visit to Colombia, arguing that "legalization is not the answer." He added, "The capacity of a large-scale drug trade to dominate certain countries if they were allowed to operate legally without any constraint could be just as corrupting, if not more corrupting, than the status quo."

Carolyn Kaster / AP

Leonard Pitts Jr. of the "San Jose Mercury News" points out that the drug trade already has dominated Colombia. And even in the absence of the cartels, former drug traffickers make money there selling people, using the same infrastructure they used to sell drugs. There's a distinct possibility that while Obama was railing against drug kingpins, his Secret Service agents were essentially supporting them.